Now that the Bloomberg administration has snatched Governors Island from New York’s paralytic and destitute state government, the city can do something radically old-fashioned: build a big new park and hope that greenbacks will follow greenery instead of the other way around.

Think of Governors Island as a pair of conjoined pancakes, one bumpy, the other flat. The bumpy pancake, which faces north toward lower Manhattan, contains fortifications run by the National Park Service and a landmarked historic district of old military buildings that can be spiffed up but not transformed. Pancake No. 2, a flat, unpromising wasteland, will be partitioned between a core of sculpted parkland and blank patches available for private development. So far, the island has attracted plenty of fantasies—an NYU outpost, a conference center, a theater, a hotel—but no developer has offered any concrete proposal. So the agency that administers the island commissioned the Dutch architectural firm West 8 to fashion the park first and let future buildings form around it. The result would be 87 acres of public space that’s truly public, including ball fields with views of the Statue of Liberty and man-made hills and dales.

For decades, new open areas have been born as by-products of business deals and carved out of leftover acreage into awkward, stingy shapes. A 1961 law traded space in the sky for space on the ground in midtown: Companies that built public plazas could pack an extra 20 percent onto their towers’ height. The city and state have funded the construction of Hudson River Park, but not its upkeep. The Bloomberg administration’s rezoning of the Greenpoint-Williamsburg waterfront forced developers to adorn their high-rises with a strip of greenery. The financing for Brooklyn Bridge Park presupposed a phalanx of condos and a big hotel. The High Line was predicated on its power to boost property values. Gradually, a new park evolved from a public good to just another real-estate amenity, like closet space.

If that doctrine had governed New York during its most frantic periods of growth, this would be a far less breathable city. Central Park and Prospect Park exist because nineteenth-century aristocrats and politicians concurred that creating a place where urban multitudes could immerse themselves in nature was a civic undertaking, not a business venture. In the thirties, Robert Moses expanded Riverside Park as a scenic haven from industrial grime.

The future of Governors Island is shaped less by lofty aspirations than by a history of puzzled neglect. Since nobody could quite figure out how to make money there, it has been lying in a state of suggestive dilapidation. During the years when the state government festered, funding dried up, and delays mounted, the island turned into a real-life laboratory of leisure. Leslie Koch, president of the agency that administers the island, has used her paltry budget to entice a growing stream of visitors and to experiment with low-tech attractions like hammocks and free bicycles. The once forbidden island has quietly insinuated itself into the public’s consciousness, and the lessons learned from observing New Yorkers at play have made their way into the future park’s design—which is why the Dutch architect Adriaan Geuze’s design for the park includes a “Hammock Grove.”

If the city’s initiative winds up luring investment, then all of Koch’s watching, waiting, and tinkering will eventually yield a private project that began with a public park—a campus or complex that molds itself to the contoured land and architecture that takes its cues from pathways, hills, and people. Governors Island could wind up being the most conspicuously virtuous legacy of Mayor Bloomberg’s third term.